The purpose of this proposal is to investigate the factors at work in the production of exercise-induced asthma by using a series of experiments that have been designed to gain insights into multiple aspects of its pathophysiology. A large number of asymptomatic asthmatics will be asked to run on a treadmill while multiple parameters of lung function are measured prior to, during, and serially after completion of the work load. The purpose here is to determine: (1) if exercise is a specific trigger of asthma that is operable only in selected patients, or a general one that causes changes in all; (2) the factors influencing the response; and (3) the site of action. Those subjects who respond will be restudied on that and subsequent days in order to determine the reproducibility of these phenomena. When this is known, they will be further investigated to try to come to some understanding of the possible mechanisms at work, and the effects of therapy. This will be accomplished by looking for the release of slow reacting substance of anaphylaxis into arterial and venous blood, and testing the effects of methylxanthines, sympathetic agonists and disodium cromoglycate. The response to administered carbon dioxide, atropine, oxygen and bicarbonate will also be evaluated.